Gun sound moderator

ABSTRACT

A gun sound moderator  30  has an external moderator cylinder wall  50  inside which is a series of stages  54  each having a baffle  32  formed with a concentric hole  46  which is concentric with the cylinder wall  50  and a deflector  38 , gas passing through the concentric hole being deflected by the deflector  38  so as to move with a radial component towards an end to move with a circulatory motion along/around inside the moderator cylinder wall  30  so as to achieve improved heat transfer from the gas through the moderator cylinder wall and into the ambient atmosphere outside the gun sound moderator so as to achieve cooling of the gas so as to reduce its volume and controlled gas release to atmosphere, so as to achieve a relatively quiet report/noise when a projectile  20  is fired through the gun sound moderator.

FIELD OF THE INVENTION

The present invention relates to gun sound moderators, including those for use on guns and firearms, e.g. small arms.

BACKGROUND OF THE INVENTION

Gun sound moderators are used to make the report from the end of gun barrel's muzzle quieter so that the operators of guns and the surroundings have limited exposure to loud noise. Ideally, gun sound moderators should combine quietening of the report of the gun together with small size and lightness. Small size is preferred to ensure that gun sound moderators do not obscure the target through the sighting system of the gun and lightness is preferred so as to not overly impact the balance and handling of the gun to which the gun sound moderator is attached. Since the gun sound moderator is located at the end of the gun, this can have a significant impact due to the weight of the gun sound moderator being at a distance from the place at which the gun is held and high weight can adversely impact the package weight of the gun plus the gun sound moderator.

Gun sound moderators are typically cylindrical with a concentric hole through them, the moderator being attached, by some means, to the end of the gun barrel such that a concentric hole through the centre of the gun sound moderator is in alignment with the bore of the gun barrel such that the projectile leaving the gun barrel can pass directly through the gun sound moderator, the projectile leaving the muzzle of the gun barrel and passing through the concentric hole of the gun sound moderator. In doing so, the report (noise) of the gun is reduced. Gun sound moderators typically use a series of baffles so as to reduce the report/noise of the gun when fired, the baffles reducing the report by interfering with the exit of the high-pressure gas that has been generated to push the projectile from the barrel.

To achieve a level of report/noise reducing properties, however, known gun sound moderators tend to be relatively large. Thus, it is difficult to produce a small, light gun sound moderator that is also quiet.

SUMMARY OF THE INVENTION

The present invention aims to alleviate at least to a certain extent the problems of the prior art.

According to one aspect hereof there is provided a gun sound moderator which is adapted to mount at a gun barrel muzzle, the moderator having a body, the body having a longitudinal axis and having a moderator cylinder wall having an internal surface within which are a plurality of moderating stages, each stage having (A) a baffle formed across and inside the cylinder wall and having a concentric hole which is concentric with the moderator cylinder wall; and (B) a deflector adapted to deflect gas flow from the concentric hole to move with a radial component so as to impact the internal surface of the moderator cylinder wall and be guided for circulation around the same.

Advantageously, the gas leaving the barrel upon firing a projectile from the gun is deflected within the body such that the gas is deflected to move with a radial component out to and in and around the internal surface of the cylinder wall of the body before finally exiting the moderator. The motion of gas flow around the internal surface of the cylinder wall may substantially or at least generally or partly comprise a toroidal motion. This allows for a much smaller and lighter gun sound moderator than those available in the prior art that with the same, or better, report/noise reducing properties.

The report/noise of a gun is a result of the pressure wave generated by the high-pressure, hot gas leaving the barrel of the gun at the muzzle upon firing a round/projectile from the gun, for example a rifle or other cartridge. Reduction in the pressure/volume of the gas has a relationship in the reduction of the report/noise of the gun.

The gas may be emitted from a hole through a baffle as a generally conical jet, then being deflected within the moderator so as to have a radial motion, or a motion first with a radial component outwardly to the internal wall, and then a circulatory or toroidal motion around inside the internal wall, within the body of the moderator so as to work to reduce the report/noise by two means. Firstly, the gas passing through the moderator spends more time than in prior art moderators in contact with the material of the moderator, cooling the gas. Rotating the gas around inside the moderator, rather than merely interfering with its progress within the moderator, ensures that the gas, which is hot since it is a product of exothermic chemical reaction due to firing of the cartridge or round, spends more time than in prior art moderators in contact with the material of the construction of the moderator, particularly of the moderator cylinder wall where heat transfer to the atmosphere may occur, and the gas is therefore cooled further than would normally be possible in a given volume with known gun sound moderators. The radial movement and circulation of the gas and the internal construction of the moderator ensure that the hot gas spends as much time as possible within the external moderator cylinder wall of the moderator. It is the external surface of the moderator cylinder wall which has the greatest ability to lose heat due to its direct contact with ambient temperature air which allows the gun sound moderator to continue to work efficiently. Cooling the gas reduces its volume, as described by Charles's law. The volume of gas can approximate to being proportional to the temperature of the gas and reducing the temperature of the gas within the gun sound moderator reduces the volume of the gas and therefore the pressure wave which creates the report/noise. Secondly, deliberately rotating the gas within the gun sound moderator ensures that the gas is retained within the body of the gun sound moderator before finally exiting in a controlled way over a greater period of time compared to that of the uncontrolled release from a gun barrel alone.

The deflectors in different stages inside the gun sound moderator may be positioned rotated apart relative to one another at each stage. However, they may not be. The deflectors in at least one said stage may be arranged to cause a circulatory or toroidal gas flow within the moderator which is in a clockwise direction, or in an anti-clockwise direction, when seen looking along in the forward direction of movement of a projectile through the moderator. Different stages within the moderator may rotate the gas in opposite directions in some embodiments.

When deflectors in different stages are positioned rotated apart relative to one another, the deflectors may serve a second purpose in addition to their deflection function: the deflectors may be structural. In particular, when stages have baffle plates extending across a body of the moderator, the deflectors may ensure that substantially all of the area of each baffle plate is supplemented in thickness by the deflectors, noting that the deflectors may be located on both sides of the baffles plates to achieve this. Thus, the deflectors may serve to enable a core of the moderator to withstand the substantial pressures generated when firing projectiles.

Each stage may have one or more than one said deflector. In this case, the gun sound moderator may have two said deflectors at each stage which are positioned angularly rotated 180° relative to one another about the longitudinal axis of the body.

Each deflector, when viewed cutaway in a direction from a side of the body, may look straight and angled at approximately 45° to the longitudinal axis of the body. Alternatively, each deflector may be curved and with a radius in a section viewed across the longitudinal axis of the body.

According to a further aspect hereof, there is provided a gun having a gun barrel with a muzzle and a gun sound moderator as set out in the first aspect hereof mounted at the muzzle.

According to a further aspect hereof, a gun sound moderator has an external moderator cylinder wall inside which is a series of stages, each having a baffle formed with a concentric hole which is concentric with the cylinder wall and a deflector, gas passing through the concentric hole being deflected by the deflector so as to move with a radial component towards and then to move with a circulatory motion along/around inside the moderator cylinder wall so as to achieve improved heat transfer from the gas through the moderator cylinder wall and into the ambient atmosphere outside the gun sound moderator so as to achieve cooling of the gas so as to reduce its volume and controlled gas release to atmosphere, so as to achieve a relatively quiet report/noise when a projectile is fired through the gun sound moderator.

A further aspect provides a gun sound moderator which is adapted to mount at a gun barrel muzzle, the moderator having a body, the body having a longitudinal axis and having a moderator external wall having an internal surface within which is at least one moderating stage, each stage having (A) a baffle formed across and inside the external wall and having a gas passage formed for the flow of gas therepast; and (B) a deflector adapted to deflect gas flow from the gas passage to move so as to flow towards the inside of the moderator external wall and be guided for circulation around the same.

The moderator external wall may be cylindrical, such as circularly cylindrical. In other embodiments it may be tapered or stepped in cross-dimension or diameter.

The gun sound moderator may include a plurality of said stages.

The gas passage may comprise a hole formed through the baffle and concentric with a centre longitudinal axis of the body of the gun sound moderator.

Each deflector may include a first wall surface which is curved, for example concave, so as to deflect gas travelling from the hole towards the external wall. In this case, the first wall surface may be an at least part circularly cylindrical first wall surface and oriented with a longitudinal direction thereof substantially perpendicular to the central longitudinal axis of the body. The first wall surface may be curved in other ways in other embodiments such as by having a parabolic or hyperbolic cross section, or a curved cross section which varies in a radial and/or axial direction.

Each deflector may include a second wall surface which is planar or substantially planar and which is oriented substantially parallel to the longitudinal direction of the at least part circularly cylindrical first wall surface.

Each deflector may include a second wall surface which is planar or substantially planar and which is oriented substantially parallel to the longitudinal axis of the body.

Each deflector may include a third wall surface, the third wall surface together with the external wall forming a passage therebetween for the flow of gas therethrough with a circulatory or rotational motion around inside and guided by the external wall.

The third wall surface may have a curved profile and may substantially comprise part of a surface of revolution whose imaginary axis of rotation is on a convex side of the curved profile.

The curved profile may be substantially semi-circular.

The gun sound moderator may have a toroidal passage formed within the body for toroidal gas flow therethrough, the passage including at least one flow guide extending along within the toroidal passage.

The at least one flow guide may comprise a fin or vane.

The fin or vane may be generally planar.

At least one said fin or vane may extend in a direction generally perpendicular to or perpendicular to the longitudinal axis of the body, or may be oriented at a slant thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side cutaway view of a typical known prior art gun sound moderator with baffles, together with a gun barrel/muzzle;

FIG. 2 shows a side cutaway schematic view of a first embodiment of a gun sound moderator in accordance with the invention;

FIG. 3 shows a schematic end view cross-section along a longitudinal axis of the moderator shown in FIG. 2;

FIG. 4 schematically shows part of a gun sound moderator as shown in FIGS. 2 and 3, but with a modified deflector;

FIG. 5 shows an isometric view of part of a second embodiment of a gun sound moderator in accordance with the invention;

FIG. 6 shows a further isometric view of the gun sound moderator of FIG. 5;

FIG. 7 shows a gun with a gun sound moderator as shown in FIGS. 2 and 3, or as modified with reference to FIG. 4 or as in FIGS. 5 and 6, mounted at the muzzle of the gun barrel thereof;

FIG. 8 schematically shows in isometric a section, in a plane coincident with a longitudinal axis of a body of the gun sound moderator of FIGS. 5 and 6, through a toroidal flow path of gas within a stage of the gun sound moderator; and

FIG. 9 shows a schematic side elevational cross section through the gun sound moderator of FIGS. 5, 6 and 8, modified by the inclusion of flow-guiding fins within a toroidal flow passage thereof.

DETAILED DESCRIPTION

FIG. 1 shows a gun barrel 10 with a gun barrel muzzle 12 and a typical known baffled gun sound moderator 14 with baffles 16, the gun sound moderator 14 being mounted at the gun barrel muzzle 12. Upon firing a projectile 20 with a direction of travel (longitudinal moderator axis) 22 through the gun barrel 10 and gun sound moderator 14, high velocity hot gas with a direction of travel depicted by arrows 24 passes through the gun sound moderator 14 with turbulent gas flow as depicted by arrows 26. As the gas from the gun barrel 10 exits the barrel 10 and passes within the moderator 14, it expands, approximated to a cone (as shown by arrows 24) in FIG. 1, with a velocity in the direction of an exit 28 of the gun sound moderator 14 furthest from the gun barrel muzzle 12. The baffles 18 within this typical known moderator “strip” the high velocity gas from the projectile 20, as shown schematically in FIG. 1.

In one embodiment in accordance with the invention as shown in FIG. 2, a gun sound moderator 30 with baffles 32 is mounted to a gun barrel muzzle 34 of a gun barrel 36 and is provided with deflectors 38 whereby, when a projectile 40 with direction of travel 42 is fired through the gun barrel 36 and gun sound moderator 30, along a longitudinal axis 44 of the gun sound moderator 30, gas flows from concentric hole 46 in a baffle 32 of the gun sound moderator 34 first along arrow 1 to deflector 38 then is deflected off the deflector 38 in a radial direction 2, or at least a direction with a radial component. Then, as shown in FIG. 3, the gas is, as shown by arrow 3, subjected to circulation around and guidance from an internal surface 48 of moderator cylinder wall 50 with an external surface 52.

Thus, as shown in FIG. 3, at least some of the gas, upon firing the projectile 40, exits the concentric hole 46 generally in the form of a conical jet and travels along as schematically depicted by arrow 1, at least some of the gas impacts radial deflectors 38 and changes direction so as generally to have a radial component travelling generally in the direction depicted by arrow 2. At least some of this flow then impacts the internal surface 48 of the moderator cylinder wall 50 to be deflected to provide at least some of the gas with a generally circulatory or toroidal motion or a circulation guided from internal surface 48 of moderator cylinder wall 50, before passing to a next stage 54 of the gun sound moderator 34 with a further baffle 32 and deflectors 38.

For clarity in FIG. 2, the deflectors 38 are shown in the same plane but they may be positioned rotated apart at each stage 54 or have more than one deflector 38 in each stage 54. FIG. 3 shows two deflectors 38 which are located 180° apart with respect to one another. Each stage 54 includes a baffle 32 with its concentric hole 46 and the downstream part of the cylinder wall and deflectors 38 before the next baffle 32.

FIG. 2 shows the deflectors 38 as approximately 45° straight items. In practice, these can be shaped and angled for better efficiency by looking at the multiple angles of the gas flow expanding through the concentric hole 46. Each angle will have a corresponding angle to which the deflector is shaped so as to ensure that the gas is deflected in a radial fashion at an approximately 90° angle to the movement of the projectile 40. In practice, this means that the deflector may be curved in shape and for the purposes of making a practical gun sound moderator is a radius.

This is shown in FIG. 4 with only a single stage 54 for clarity. FIG. 4 shows the projectile 40 with direction of travel 42 and the embodiment has radial deflectors 38, so this is an example of an advanced shape of the radial deflector 38 and shows how gas is sufficiently directed to travel in a radial way inside a single stage 54 of the gun sound moderator 30.

In a further embodiment in accordance with the invention, FIG. 7 shows a gun sound moderator body 100 mounted to a muzzle 102 of a barrel 104 of a gun 106. FIGS. 5 and 6 show the body with a circularly cylindrical external wall 108 thereof removed to reveal a central core 110 thereof. The central core 110 includes a threaded attachment mounting flange 112 for mounting the body 100 to the muzzle 102 and a set of four angularly spaced tension arms 114 connecting the flange 112 to a first of four baffle plates 110, each baffle plate 110 having a circular edge 134 which, together with a circular outer edge of the flange 112 and an exit flange 130 may be sealingly engaged against the inner surface 101 of the circularly cylindrical external wall 108, using mechanical or other means (not shown). The moderator body is therefore preferably sealed apart from where the projectile enters and leaves it.

The arms 114 form a pre-chamber 116 whose design may vary in other embodiments, for example extending back over the muzzle 102. The pre-chamber may thus form a pressurisable plenum in advance of the moderating stages of the moderator.

Each baffle plate 110 comprises a circular disc with a central hole 120 passing through it for the passage of hot gas through the moderator body 100. Each baffle plate 110 is part of a stage 103 of the moderator body 100 which also includes two deflectors 105 linking the stage to the next downstream stage or the final exit flange 130. The two deflectors 105 of each stage 103 are the same as one another and positioned rotated angularly 180° relative to one another. The deflectors 105 of adjacent stages are positioned rotated angularly 90° relative to one another. This can enable the material of the deflectors to perform a second task in addition to gas deflection, namely to provide mechanical strength to the core of the moderator by ensuring relatively thick material, so a strong construction, in all regions of each baffle plate 110. These constructions could differ in other embodiments. For example, three deflectors could be provided located 120° apart from one another. Each stage could have different numbers of deflectors, e.g. any number between one and about six, and the deflector(s) in different stages may have different axial lengths and dimensions to one another.

Each of the two deflectors in FIGS. 5 and 6 has three wall surfaces 122, 124 and 126.

The first wall surface 122 is curved and this surface is substantially part of the surface of an imaginary circular cylinder, the axis of which is perpendicular to or substantially perpendicular to and may substantially intersect with or actually intersect with the longitudinal axis 127 of the body 100. The diameter of the imaginary cylinder may be substantially the same as the distance between the baffle plates 110 located adjacent each deflector 105.

The second wall surface 124 also has a curved profile and comprises part of an imaginary surface of revolution whose centre is on a convex side of the curved profile (and may be on the longitudinal axis 127 of the body 100), the curved profile optionally being substantially semi-circular, in which case the diameter of the curved profile is or may be substantially the same as or the same as the distance between the baffle plates 110 located adjacent each deflector 105. The second wall surface 124 together with the interior surface 101 of the external cylindrical wall 108 therefore forms a passage 129 between these surfaces for the flow of gas therethrough with a circulatory rotational motion around inside and guided by the inside surface 101 of the external wall 108.

The third wall surface 126 is substantially planar or planar, lying parallel to or substantially parallel to the longitudinal axis 127 of the body 100. The plane of the third wall surface 126 may also be substantially perpendicular to the axis of the imaginary circular cylinder of the first wall surface 122. Parallel to the third wall surface 126 but facing oppositely is an optional relatively small planar eyelid-shaped surface 128 on each deflector which intersects with the curved first wall surface 122. The purpose of surface 128 is to split, separate and hold apart the respective gas flows flowing towards different deflectors 105. This therefore helps ensure that the gas flows to the intended deflectors 105. The surface 128 may have other shapes in other embodiments. Dependent upon geometry of the size or stages and the number of deflectors, the surface 128 may be employed to enhance noise reduction, being sometimes used but not necessarily always in every stage. The surface 128 may be omitted entirely in some embodiments or merely from one or more stages.

As depicted by flow path arrow 140, high-pressure gas passing through each central hole 120 may first have an outwardly-flaring first path 142 to the first wall surface 122 from where it is deflected on a second path 144 with a radial component out to where it reaches the interior surface 101 of the cylindrical external wall 108 and is deflected into a circulatory or rotational motion path 146 along the interior wall 101 and through the passage 129 before passing radially inwardly again and out through the next central hole 120 of the moderator body 100 in one of the baffle plates 110 or the end flange 130. The circulation of the flow, including through the passage 129, ensures good cooling of the flow and therefore a reduced report (noise) when the gun 106 is fired.

As flow arrow 148 shows, flow exiting the internal hole 120 in the direction of the planar third wall surface 126 of each deflector is not significantly deflected by the third wall surface 126 because the third wall surface 126 substantially intersects with the longitudinal axis 127 and this flow is therefore drawn around into the passage 129 together with the flow which has been deflected by the curved first wall surface 122. Although some of the flow passing generally along the flow arrow 140 or alongside it may mix with flow exiting from the second of the two passages 129 in the same stage 103, the construction overall permits a substantial rotational circulation of flow which is toroidal in nature and/or form around the passages 129 before the pressure differential across the stage 103 and between the stage 103 and to the next stage 103 forces the flow to move radially inwardly and out through the next central hole 120. The way in which the planar third wall surface 126 of one deflector is adjacent to the curved first wall surface 122 therefore assists in causing rotational flow around through the two passages 129 of each stage 103. The toroidal flow is highly advantageous, permitting significant heat transfer from the gas within the moderator out to atmosphere by means of conduction outwardly through the external wall, which may conduct heat very well, such as when made of an aluminium alloy. The body of the moderator including the baffle plates 110 and deflectors 105 may also be formed of such material.

It is noted that the deflectors 105 have a second purpose, above deflection, which is structural: the deflectors 105 join baffle plates 110 of the core together and take substantial load in tension to hold the core together when the gun 106 is fired.

The construction described with respect to FIGS. 5 to 7 permits a gun sound moderator which is small and light yet which has good performance in moderating or attenuating the report of a gunshot and the shot is not heard so easily so as to limit the sound of the shot in the surrounding area. Although a supersonic projectile fired from the gun 106 may still create significant noise due to the shockwave caused by supersonic flight through air, the noise experienced by the operator firing the gun is substantially reduced.

The moderator body 100 shown in FIG. 7 may be replaced on the gun 106 if desired by the arrangement shown and described with reference to FIGS. 2 and 3 above, or as modified with reference to FIG. 4.

FIG. 8 schematically shows in isometric a section, through a plane coincident with a longitudinal axis 127 of a body of the gun sound moderator of FIGS. 5 and 6, a toroidal flow path of gas within a stage 103 of the gun sound moderator next to the inner surface 101 of the external wall 108. The section through the toroidal flow path is D-shaped but may have other shapes in other embodiments.

With the gun barrel 104 rifled so as spin the projectile, all of the deflectors 105 may be configured to create the toroidal gas spin round and through the passages 129 in the same rotational direction as the direction of projectile spin. However, in other embodiments only some deflectors may do so and some or all deflectors may create similar gas rotation in the opposite direction to projectile spin caused by rifling.

FIG. 9 shows how the passage 129 may be provided with one or more flow fins or vanes 200, 202, dotted for the purposes of clarity in FIG. 9 but in practice which may or may not be solid plates or the like, aligned with the direction of intended toroidal circulatory flow. The fins 200, 202 may be planar or curved and at least when planar may be aligned perpendicular to the longitudinal axis of the moderator body or at a slant to it as shown schematically in FIG. 9. One or more fins or vanes 200, 202 in the direction of toroidal gas flow depending on stage geometry enhances sound reduction.

Various modifications may be made to the embodiments described without departing from the scope of the invention.

Various modifications may be made to the embodiments described without departing from the scope of the invention. 

1. A gun sound moderator which is adapted to mount at a gun barrel muzzle, the moderator having a body, the body having a longitudinal axis and having a moderator cylinder wall having an internal surface within which are a plurality of moderating stages, each stage having (A) a baffle formed across and inside the cylinder wall and having a concentric hole which is concentric with the moderator cylinder wall; and (B) a deflector adapted to deflect gas flow from the concentric hole to move with a radial component so as to impact the internal surface of the moderator cylinder wall and be guided for circulation around the same.
 2. A gun sound moderator as claimed in claim 1 in which the deflectors in different stages are positioned rotated apart relative to one another at each stage.
 3. A gun sound moderator as claimed in claim 1 in which each stage has more than one said deflector.
 4. A gun sound moderator as claimed in claim 2 in which each stage has more than one said deflector.
 5. A gun sound moderator as claimed in claim 3 in which two said deflectors at each stage are positioned angularly rotated 180° relative to one another about the longitudinal axis of the body.
 6. A gun sound moderator as claimed in claim 4 in which two said deflectors at each stage are positioned angularly rotated 180° relative to one another about the longitudinal axis of the body.
 7. A gun sound moderator as claimed in claim 3 in which each deflector, when viewed cutaway in a direction from a side of the body, looks straight and angled at approximately 45° to the longitudinal axis of the body.
 8. A gun sound moderator as claimed in claim 2 in which each deflector is curved with a radius in a section viewed across the longitudinal axis of the body.
 9. A gun sound moderator as claimed in claim 5 in which each deflector is curved with a radius in a section viewed across the longitudinal axis of the body.
 10. A gun sound moderator which is adapted to mount at a gun barrel muzzle, the moderator having a body, the body having a longitudinal axis and having a moderator external wall having an internal surface within which is at least one moderating stage, each stage having (A) a baffle formed across and inside the external wall and having a gas passage formed for the flow of gas therepast; and (B) a deflector adapted to deflect gas flow from the gas passage to move so as to flow towards the inside of the moderator external wall and be guided for circulation around the same.
 11. A gun sound moderator as claimed in claim 10 in which the moderator external wall is circularly cylindrical.
 12. A gun sound moderator as claimed in claim 10 which includes a plurality of said stages.
 13. A gun sound moderator as claimed in claim 10 in which the gas passage comprises a hole formed through the baffle and concentric with a centre longitudinal axis of the body of the gun sound moderator.
 14. A gun sound moderator as claimed in claim 13 in which each deflector includes a first wall surface which is curved so as to deflect gas travelling from the hole towards the external wall, the first wall surface preferably being an at least part circularly cylindrical first wall surface and oriented with a longitudinal direction thereof substantially perpendicular to the central longitudinal axis of the body.
 15. A gun sound moderator as claimed in claim 13 in which each deflector includes a second wall surface which is planar or substantially planar and which is oriented substantially parallel to the longitudinal direction of the at least part circularly cylindrical first wall surface.
 16. A gun sound moderator as claimed in claim 13 in which each deflector includes a second wall surface which is planar or substantially planar and which is oriented substantially parallel to the longitudinal axis of the body.
 17. A gun sound moderator as claimed in claim 14 in which each deflector includes a third wall surface, the third wall surface together with the external wall forming a passage therebetween for the flow of gas therethrough with a circulatory or rotational motion around inside and guided by the external wall.
 18. A gun sound moderator as claimed in claim 17 in which the third wall surface has a curved profile and substantially comprises part of a surface of revolution whose imaginary axis of rotation is on a convex side of the curved profile.
 19. A gun sound moderator as claimed in claim 18 in which the curved profile is substantially semi-circular.
 20. A gun sound moderator as claimed in claim 15 in which each deflector includes a third wall surface, the third wall together with the external wall forming a passage therebetween for the flow of gas therethrough with a circulatory or rotational motion around inside and guided by the external wall.
 21. A gun sound moderator as claimed in claim 20 in which the third wall has a curved profile and substantially comprises part of a surface of revolution whose imaginary axis of rotation is on a convex side of the curved profile.
 22. A gun sound moderator as claimed in claim 21 in which the curved profile is substantially semi-circular.
 23. A gun sound moderator as claimed in claim 10 in which each deflector is configured to deflect gas to adopt an at least partly toroidal motion within the body of the moderator.
 24. A gun sound moderator as claimed in claim 1 which has a toroidal passage formed within the body for toroidal gas flow therethrough, the passage including at least one flow guide extending along within the toroidal passage.
 25. A gun sound moderator as claimed in claim 10 which has a toroidal passage formed within the body for toroidal gas flow therethrough, the passage including at least one flow guide extending along within the toroidal passage.
 26. A gun sound moderator as claimed in claim 24 in which the at least one flow guide comprises a fin or vane; optionally in which the fin or vane is generally planar; optionally in which at least one said fin or vane extends in a direction generally perpendicular to or perpendicular to the longitudinal axis of the body.
 27. A gun sound moderator as claimed in claim 25 in which the at least one flow guide comprises a fin or vane; optionally in which the fin or vane is generally planar; optionally in which at least one said fin or vane extends in a direction generally perpendicular to or perpendicular to the longitudinal axis of the body.
 28. A gun having a gun barrel with a muzzle and a gun sound moderator as claimed in claim 1 mounted at the muzzle.
 29. A gun having a gun barrel with a muzzle and a gun sound moderator as claimed in claim 10 mounted at the muzzle. 